700-2.14: Safety Relays - Rockwell Automation

1 Safety Relays (Catalog Number 700-Z) product DataContentsThis product data contains:SectionPageIntroduction2 What is a Safety Relay?3 Positive Guided Relays4 Redundant, Self Monitoring Circuit5 Safety Relay Operating Principle7 Safety Relay Benefits9 Safety Relay Applications11 Emergency Stop Function11 Safety Gates15 Two Hand Control18 Expander Modules22 Additional Applications24 Higher Current Applications and Additional Safety Outputs (AuxiliaryRelays)25 Connecting to DeviceNet28 Troubleshooting Guide29 overview of Safety Standards31 Specifications and Approximate Dimensions36 Appendix382 Safety RelaysSafety Relays are becoming a popular component in Safety systems, due toincreasing regulations and attempts to safeguard operators from applied correctly, Safety Relays will detect failures in output andinput devices, as well as internal failures, allowing power to be removedfrom a load, even if a contact is welded, and prohibit a subsequent restartof the load until the failure is corrected.

2 Safety Relays are just onecomponent in the Safety control system. All components in the systemmust be chosen and applied correctly, to achieve the desired level ofoperator publication describes the operation of a Safety relay, discussesapplications, outlines some of the standards that reference Safety , andprovides specifications for Allen Bradley Safety Safety relay technical and application support, call Literature for Safety Related Issues: Understanding the Machinery Directive, publication SHB 900 A Global Reference Guide for Reading Schematic Diagrams,publication 100 Industrial and Safety Relay Selection Guide, publication 700 Safety Relay Color overview , publication 700 Modular Control System, publication 100C Safety Interlock and Cable Pull switches Color overview , publication802SS Stack Light Selection Guide, publication 855T Flexible Solutions In Control and Load switches , publication 194 30mm NEMA Style Push Button Selection Guide, publication 800 22mm IEC Style Push Button Selection Guide, publication 800E RelaysA Safety relay: Is designed with an internal circuit that will allow power to beremoved from a load even if an internal contact welds.

3 The internal circuit is redundant and self monitoring, usingmultiple, positive guided Relays . Monitors faults in the Safety relay, and the input ( Start and StopButtons) and output ( Auxiliary Relay) devices. Typically replaces the relay (often a master control relay) that interfacesbetween input devices and contactors or starters. Can be ordered with different numbers of contacts, like any other relay. The contacts are called monitored outputs or Safety outputs ,and have two or more contacts in series to achieve redundancy foreach load (refer to figure 1). Is designed to meet requirements for Safety categories as outlined inEuropean Norm EN 954 and EN SymbolsIEC Symbols per IEC 617 7 Standard RelayContactSafety OutputStandard RelayContactSafety OutputPositive GuidedContactsPositive GuidedContactsFigure 1 What Is a Safety Relay?4 Safety RelaysAlso called All or Nothing Relays with Positively Driven Contacts.

4 Relays of this type have contacts that are mechanically connectedtogether, such that if a normally open (NO) or make contact remainsclosed, a normally closed (NC) or break contact can not re , if a NC contact fails to open upon energizing the relay, theNO contacts shall not close. This is outlined in ANSI and Guided Relay ContactsStandard Relay ContactsNormally Open (Make)Contacts are ClosedNormally Closed(Break) Contact is OpenNormally Open (Make)Contacts are ClosedNormally Closed(Break) Contact is OpenNormally Open (Make)Contact is Welded ClosedNormally Closed (Break)Contact Remains OpenNormally Open (Make)Contact is Welded ClosedNormally Closed (Break)Contact Can Return ToClosed StateRelay is De EnergizedRelay is De EnergizedRelay is EnergizedRelay is mmFigure 2 The positive guided feature is necessary in the circuit design to ensurethat the circuit does not re close after a fault.

5 Redundant contacts wired ina series ensure that the power can be removed from the load, even if acontact has welded. Refer to the redundant, self monitoring circuit (page5) for a more extended with positive guided contacts can be the standard panel or DIN railmount varieties, or printed circuit board mount, like those found insidesafety Guided Relays5 Safety RelaysThe figure below shows a typical control circuit with a master controlrelay. This circuit works fine, if we can assume that CR(b) never welds. IfCR(b) were to weld, pushing the E Stop button will not remove powerfrom the motor (M). If the motor drives a blade or cutter, the hazard cannot be disabled. If the operator assumes the blade has stopped and entersthe area, he could suffer serious ButtonCR(a)CRStartCR(b)MOLL1L2 Figure 3If a process can cause serious harm to an operator, it is a likely candidatefor a redundant, self monitoring control circuit, like the one shown is similar to the internal circuit found in an Allen Bradley safetyrelay.

6 It is redundant because it uses three Relays (redundancy requires twoor more of a given component). It is self monitoring or self checkingbecause it allows power to be removed from a load, even if a contactwelds, but will not allow a subsequent restart until the fault is (a)StopStartCR3CR1(a)CR2(b)CR1(b)CR2(c)C R1(c)CR3(b)CR1CR2CR1(d)CR2(d)CR3(c)Chann el 1 Channel 2L1L2 MCR2(a)Figure 4 Redundant, Self MonitoringCircuit6 Safety RelaysNormal OperationWhen the E Stop is pulled up, power flows through CR3(a) and CR1(b)energizing the coil CR2. When this coil is energized, the NO contactsCR2(a), CR2(b), and CR2(c) close and energize coil CR3. The NO contactCR3(b) closes and holds the coil CR3 energized. The device is now armed and ready .When the operator pushes the start button, coil CR1 energizes. CR1(a)closes to hold in CR1. Then the NC contact CR1(b) opens and disconnectspower from coil CR2.

7 The final state is: coil CR1 on, coil CR2 off, andcoil CR3 on. This condition allows the contacts of the output line [CR1(d),CR2(d), CR3(c)] to be closed and the load energized. The output line isalso called the monitored output or the Safety output . The terminologyis the same for Safety relay Examples Start Button Welded (Fault):If the start button is welded ( held energized) when the E Stop isreset, then coil CR2 will not energize because the circuit is nevercomplete in the rung with CR3(a) and CR1(b). Since coil CR2 can notenergize, it is not possible to pull in coil CR3 or CR1 because CR2(c)will not close. Output CR2(d) Welded (Fault):After resetting the E Stop, coil CR2 will energize, but since contactCR2(d) is welded and CR2 is positive guided, the NO contact ofCR2(c) will not close, thus coil CR3 can not energize and the systemcan not be started again. Similarly, if CR1(d) welds, CR1(b) will beheld open.

8 If CR3(c) welds, CR3(a) will be held open. Both situationsprevent coil CR2 from energizing, so the system can not be rearmed. E Stop Failure:If there is a short across the channel 2 contact block of the E Stop,then CR3 will not de energize, but CR1 will open the load. Restart isnot possible since CR3(a) did not re close preventing CR2 fromre energizing. Similar fault detection is provided for the channel 1E Stop circuit via CR1(b).7 Safety RelaysThe Safety relay has a similar circuit to the one described in figure 5 shows the wiring for a typical category 4 E Stop (two contacts or channels on the E Stop). The timing diagram in figure 6, shows thesequence of events when the E Stop is closed and the reset button DiagramA1T11T12T31T34T22T351323334353617 3A2X1X2T3314243444546274T32B1B2(+)( )K3K2K1K1K2K3cChannel 1 (T11-T12)Channel 2 (X1-X2)E-StopResetWiring Diagram and logic circuit for700-ZBR520-- And 700-ZBR100--Figure 5 Safety Relay OperatingPrinciple50 msecMaxLegend018 Safety RelaysE Stop OpenAll Relays arede energizedE Stop Reset Relay K2 is energized K2 NO contacts between T22 and relay K3, and between T32 and relay K1 are closed Relay K3 is energized ashort time later K3 NO contact between T32 and relay K1 closesReset ButtonDepressed Reset NC contact opens Reset NO contactcloses Relay K1 is energized Relay K2 begins to time outK2 De Energized K2 NC contacts in the output circuits close Output circuits are closed and loads can be energized All signaling circuits openReset Button IsReleased No specific time duration neededE Stop Channel 1(T11 T12)E Stop Channel 2(X1 X2)Reset NO(T31 T32)Reset NC(T31 T34)

9 Relay K1 Relay K2 Relay K3 Safety Outputs13 14, 23 24, 33 34,43 44, 53 54 Signal output61 output73 69 Safety Relays Enhanced Operator Safety When applied and wired correctly, common control system faultsthat could lead to a hazardous situation can be minimized throughthe redundancy and self-monitoring provided by the Safety Relays allow the operator to remove power from the loadeven when a fault occurs. This can reduce potential injuries andlost workdays. Obviously, worker Safety is the first concern, butsafety Relays may also lead to reduced compensation and legalissues. Enhanced Machine Performance Safety Relays can minimize costly downtime and replacementparts costs, by allowing the machine to perform according to itsintended design. Operator injuries result in machine damage thatmust be repaired. The maintenance time and replacement partsadd to operating costs. If downtime is minimized, the process works according to designand maximizes productivity and efficiency for the business.

10 Easier Troubleshooting LEDs provide clear diagnostics to quickly identify faults LEDsindicate power, run, input short, input fault, and output to the Troubleshooting Guide section (page 29) for acomplete diagnostic overview . Simplified Installation Clearly marked terminals DIN rail mount Small, with core circuit wires contained in the box Flexible Configurations Multiple voltages in a single unit 120V AC, 24V AC/DC Multiple function versions, or E Stop only reduce stockedparts, simplify parts with a multiple function unit (includesE Stop, Safety gate, and two hand control) Expander units available, for additional outputs Auxiliary Relays can be used for higher current applicationsSafety Relay Benefits10 Safety RelaysExample shown is 90mm wideMultiple functions in a single unit (E Stop, Safety gate, light curtain, two hand control)DIN Rail MountableTroubleshooting LEDsMultiple Voltages in a Single Unit(Available in 24V DC Only)